This work presents the investigation, at room temperature, of Zn2TiO4samples containing Ni2+ ions as substitutional impurities. Samples with molecular formula Zn2(1-x)Ni2xTiO4, where x = 0.00, 0.0007, 0.001, 0.0013, 0.002 and 0.003, in which Zn2+ ions were replaced by Ni2+ ions, were prepared through solid-state method, crystalline data were obtained by X-ray diffraction, the elemental composition was determined by X-ray fluorescence and the optical properties were investigated through photoluminescence and photoacoustic techniques. The photoluminescence spectra showed broadbands from 640 nm to 800 nm. The emission of the Zn2(1-x)Ni2xTiO4 samples was assigned to the overlapping of the Ni2+and the Zn2TiO4 emission. The most intense photoluminescence signal was obtained with excitation radiation at a wavelength of 360 nm for the sample with x = 0.001. The photoacoustic spectra showed absorption bands characteristic of semiconductor materials due to the host Zn2TiO4. The energy bandgap of the Zn2(1-x)Ni2xTiO4was obtained from photoacoustic absorption spectra.

In the present work we propose the use of weighted Bregman distances in the construction of regularization terms for the Tikhonov functional applied for the formulation and solution of the inverse problem of photoacoustic spectroscopy. Test case results demonstrate that better estimates were obtained for the simultaneous estimation of the thermal diffusivity and optical absorption coefficient using, as synthetic experimental data, the information on both the amplitude and phase-lag of the temperature at the interface sample-gas between the material under analysis and the air chamber of the closed photoacoustic cell.